Glass fibers are manufactured from various raw materials combined in specific proportions to yield a desired chemical composition. This collection of materials is commonly termed a “glass batch.” To form glass fibers, typically the glass batch is melted in a melter or melting apparatus, the molten glass is drawn into filaments through a bushing or orifice plate, and a sizing composition containing lubricants, coupling agents and film-forming binder resins is applied to the filaments. After the sizing is applied, the fibers may be gathered into one or more strands and wound into a package or, alternatively, the fibers may be chopped while wet and collected. The collected chopped strands may then be dried and cured to form dry chopped fibers or they can be packaged in their wet condition as wet chopped fibers. The fibers, in turn, may be used to reinforce plastics and various other structural and non-structural products.
The composition of the glass batch and the glass manufactured from it are generally expressed in terms of percentages of the components and are mainly expressed as oxides. Compounds such as SiO2, Al2O3, CaO, MgO, B2O3, La2O, Nb2O5, Ta2O5, ZrO2, 2O3, Li2O, Na2O, GdO3, BaO, SrO, ZnO, ZrO2, P2O5, GeO2, WO3, Fe2O3, fluorine, and SO3 may be used to form a glass batch. Numerous types of glasses may be produced from varying the amounts of these oxides, or eliminating some of the oxides in the glass batch. Normal reinforcement glasses such as R-glass, E-glass, S-glass, A-glass, C-glass, and ECR-glass may be formed from certain combinations of the oxides. In addition, optical glasses having a desired refractive index can be produced by choosing oxides for the glass batch. The glass composition controls the forming and product properties of the glass. Characteristics of glass compositions include the raw material cost and environmental impact.
High refractive index glasses and use thereof in optical lens applications are known in the art. However, conventional optical glass fibers are unable to be formed by conventional fiberizing techniques because they lack sufficient viscosity above their crystallization temperature to be formed into fibers. Thus, although high refractive index glasses exist, there remains a need in the art for glass compositions that possess a high refractive index, an Abbe number and a coefficient of thermal expansion that is appropriate for the reinforcement of high refractive index plastics, and a viscosity above the liquidus temperature that is sufficiently high to permit the formation of fibers using conventional fiber forming techniques.